Inevitably, year-end lists invite plenty of debate and criticism, and Scientific American's is no exception. Certainly, we could have included the discovery of new worlds beyond our solar system, including Kepler 22 b, an exoplanet in the "Goldilocks" zone of habitability, as well as the first known Earth-size exoplanets. Or noted the accumulating evidence suggesting that hydraulic fracturing, or fracking, to retrieve natural gas is likely to contaminate water supplies. (Final New York State regulations, expected in mid-2012, could determine the future of fracking in the U.S.)

Some of our top choices could very well have an immediate effect on our lives. The impact of others may not be felt for years. Some discoveries may vanish altogether. We'll just have to see how things turn out in the years ahead. But no matter what, 2011 held big surprises in science and technology.

IBM's Watson Computer Wins on Jeopardy!

In February IBM's Watson capitalized on its advanced natural language–processing, information retrieval and machine-learning capabilities to soundly defeat two highly accomplished Jeopardy! champions—Ken Jennings and Brad Rutter—at their own game.

As far as conversing with computers, most people will be able to relate to the Siri voice-activated navigator on Apple's iPhone 4S this year before they get a chance to interact with anything as sophisticated as Watson. At least the conversation has begun.—Larry Greenemeier